Semiconductor materials are widely used in electronic and optoelectronic applications such as semiconductor chips, solar cells, light emitting diodes (LED), high-power semiconductor devices, power RF devices, flexible electronics, etc. Many of these applications are made by depositing a thin film on a substrate including foreign material, for example, depositing a thin film of Titanium on an amorphous substrate. Amorphous substrates, however, have no long-rang structural order that typically characterizes a crystal, causing many atoms to form undesirable bonding orientations and significantly decreasing the crystalline quality along with negatively impacting electronic properties of the semiconductor materials. As such, lack of long-range order in the amorphous substrate poses challenges on deposition of the thin film in order to achieve long range order or single crystal structure.
Thin semiconducting films are usually deposited on the amorphous substrate using molecular beam epitaxy (MBE) or metal organic chemical vapor deposition (MOCVD) techniques, and in some cases using atomic layer deposition (ALD) or atomic layer epitaxy (ALE). By using these methods, however, not all atoms, ions, or molecules have an opportunity to organize themselves into regular arrangements that would lead to long range order of sufficient high crystalline quality. The latter is typically described in terms of crystal size, grain size, carrier lifetime, and diffusion lengths. To overcome this drawback, it is desired to grow large crystals on the substrate, where large refers to average crystal size that is at least ten times greater in physical extent in comparison to typical electrical diffusion lengths in the semiconductor (e.g. average crystal size is 100 microns, and diffusion lengths are 1-10 microns, 1 micron is equal 1×10−6 meters). Zone melt recrystallization (ZMR) is a technique for growing large crystals on a substrate. In this method, a molten region, e.g., molten zone 102 as shown in FIGS. 1A and 1B, in the deposited film is heated by a heat source (not shown) to melt the deposited material in the molten zone 102. The molten zone 102 moves across the deposited film by moving the heat source in direction A with respect to substrate 104. Deposited material to be melted represented by region 106 continues entering the molten zone 102 and is melted in the molten zone 102 while material leaving the molten zone 102 is solidified and recrystallized to form a recrystallization zone 108. In other words, as the melt zone 102 passes over the substrate 104, a large solid and single crystal is left in the wake of the melt. This is the primary method of extending a small single crystal laterally using ZMR.
While ZMR is a very well-proven technique to create high quality crystalline material it may suffer from the drawback that the temperature generated for melting a portion of the deposited film may exceed the maximum temperature that can be handled by the underlying substrate. To prevent the underlying substrate from being heated to the melting point of the deposited film, the heating time may be shortened, such as by using high repetition rate pulsed lasers. However, shortening the heating time means that while solidifying, the crystal structure may grow in vertical direction rather than in both vertical and lateral directions simultaneously. Hence, epitaxial growth may be dominated in the vertical direction rather than the lateral direction resulting in patches of small grains along the substrate. The primary function of ZMR as described above, necessarily requires a single seed to originate from a single point or edge that can effectively be extended laterally.